Roller coating apparatus



Jan. 1, 1957 w. R. WHITE ET AL 2,775,954

ROLLER COATING APPARATUS Filed Dec. 14, 1955 GALE E IVADEAU ATTORNEYS United States Patent ROLLER COATING APPARATUS Walter R. White and Gale F. Nadeau, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application December 14, 1955, Serial N 0. 553,177

4 Claims. (Cl. 118-258) The present invention relates to coating apparatus of the type comprising a hopper containing a quantity of coating solution with an applicator roll immersed therein, and particularly to means for automatically removing any undesirable solid particles which might collect at thecoating point of the hopper and means for obtaining a continuous mixing of the solution in the hopper. A well-known means of applying liquid material to the surfaces of webs in a carefully controlled manner is known as roll coating. Such apparatus involves the use of an open-mouth hopper containing the coating solution in which is immersed a rotatable applicator roll. As the roll rotates, it picks up a regulated layer of solution on its periphery which it may then apply directly to the surface of a web or to a second applicator roll which in turn applies the coating to a web.

One problem which is encountered with this type of coating apparatus is the presence of solid particles in the solution within the hopper which occasionally are transferred to the applicator roll or bead and then either make an undesirable repeating or continuous mark on the coat: edweb or become transferred to the web to make an undesirable defect. Another problem is that of obtaining a continuous stirring action of the solution in the hopper to avoid certain separating effects which are characteristic of this type of coating apparatus.

. The primary object of the present invention is to provide a coating apparatus of the type comprising an applicator roll immersed in coating solution contained in an open-mouth hopper with means for automatically withdrawing any solid particles which might enter the hopper before they can be transferred to the applicator roll.

Another object is to provide such a coating apparatus with a solution circulating system which does not involve the use of any moving parts to break up a separating action in the solution which is characteristic of this type of apparatus.

Briefly, the present invention makes use of the currents of flow set up in the solution contained in the hopper by rotation of the applicator roll along with a certain solution .feed and draw-off means and a certain hopperto-applicator roll relationship to automatically remove any solid particles from the hopper before they canbe transferred to the applicator roll. In addition, the char,- acteristic flow currents of the solution in the hopper are used to obtain a mixing of the solution in the hopper, said mixing acting to break up a separating action produced in the solution within the hopper vby the normal flow currents.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings in which:

- Fig. 1 is a schematic end view, partly in section, of a conventional coating apparatus of the type with which the present invention may be combined;

Fig. 2 is a side elevation partly in section of the hopper ice and roll and showing how the solution is fed into and withdrawn from the hopper as well as how the hopper bottom is pitched relative to the roll;

Fig. 3 is an enlarged plan view of the hopper and applicator roll showing the transverse currents of flow set up in the solution in the hopper by the applicator roll when it rotates and indicating the contour lines of the surface of the solution causing such currents of flow;

Fig. 4 is an end elevational view of the hopper and roll provided with a piping connection placing the opposite sides of the hopper in direct communication in accordance with the present invention to produce a mixing of the solution in the hopper; and

Fig. 5 is a plan view of the hopper and roll and showing how the solution in the hopper is separated into two separate homogeneous volumes as the result of the current flow set up by the rotation of the applicator roll.

Referring now to the drawings, the coating apparatus generally may be a conventional one comprising an openmouth hopper, indicated generally at 10, consisting of an elongated trough with a flat base 11, end walls 13 and side walls 12 joined by a semi-circular bottom wall 14 which along with the end walls forms a reservoir for a supply of liquid coating solution S. An applicator roll 15 is rotatably mounted in the hopper by having its shafts 16 suitably journalled in the end walls of the hopper. The bottom portion of the applicator roll is immersed in the coating solution S and its top portion extends through the open mouth of the hopper. When the roll is rotated in the direction of the arrow by any suitable means, including gear 17 on the end of one of its shafts 16, a layer of coating solution S is transferred from the hopper to a bead 18 that is contacted by and coats the web 19 moved and supported by guide roller 20 which moves in the direction opposite to that of the applicator roll. As is well known in the art, instead of the applicator roll transferring the coating soluution to a bead 18 across which the web is moved for coating, such applicator roll might transfer the coating directly to the web surface or to another roll which in turn transfers the coating to the web directly or indirectly.

With this type of coating apparatus it is necessary to maintain the level of the coating solution in the hopper fairly constant, and while all sorts of solution feeding systems have been used in the past, in accordance with the present invention the solution is continuously fed into opposite ends of the hopper through pipes 22 and 22 and continuously drawn off from the center of the hopper through pipe 23. These pipes can be connected by any suitable pumping system, not shown, so that the rate at which the solution is fed to and drawn from the hopper will be such as to maintain a substantially constant level in the hopper and so that the drawn-oft solution can be recirculated to the supply rather than being discarded.

As the applicator roll 15 rotates, it tends to raise the surface of the coating solution in the hopper on the up side of the roller and depress it on the down side of the roller. In Fig. 3 the contour lines numbered 1-8 represent the level of the surface of the solution at diiferent points in the hopper, and in this figure the roll-to-hopp'er clearance is exaggerated to allow the introduction of these lines with clarity. The contour level increases with the numbers and while the units of value of these numbers is not important and may vary, the difference between them may be measured in millimeters. Since the levels want to return to their normal equal positions, currents of flow are set up in this solution in the hopper, as indicated by the broken arrows in Figs. 3 and 5. In other words, it will be observed that the solution tends to flow from the juncture point I at the center of the roll on the up side thereof around the ends of the roll in opposite directions final result is two homogeneous liquid volumes .represented diagrammatically in Fig. 5 by the two types of cross hatchings. Any end-to-end variation in feed, machine conditions, application, accidental evaporation, etc. will make theliquiddn thetwo volumes different.

We have found that if a connection :is made between contour :lines 2 and 7?, liquid will flow from the homogeneous volume "at 7' to the other homogeneous volume at .2. This is accomplished by connecting the up side of thehopper to the down sideof the hopper by a .conduit 3.0, as shown in Figs. 3 and 4. This will produce a mixing action between the two different homogeneous volumes into which the solution tends to separate as the result'of normal aotionof the roll rotating in the-solution. Similarly,.points 2 and .7 in :the hopper can'beconnected on another occasion .or 'both connections can be used at the'same time if desired.

When the currents of flow shown in'Fig. 5 are examined, it will'be-noted that any solid particles which might enter thesolution in the hopper will be swept along by the solution and tend to congregate at the junctures I and J, especially on the down side of the applicator roll 15. Depending upon many variables, the junctures J and J will be located anywhere along the middle third of the roll. However, we have found that if the bottom of the hopper is slightly pitched away from the center of the roll-in both directions, as shown in Figs. 2, 3 and 5, thenjunctures J and J will remain at'the point of smallest clearance no matter how other factors are varied. In actualpractice wehavepitchedthe bottom of the hopper from' i at the center to /8" at each end of the roll with good results. It will be .noticed by referring to Figs. 3 and 5 that even those portions of :the semicircular bottom wall 14 coming up on opposite sides of the applicator'roll 15 are pitched away from thecenter of the roll toward both ends of the hopper for best results. It follows that if the hopper instead of havinga semi-circular bottom as shown, has distinctive bottom and side walls, then each of these walls should be pitched relative to the roll as mentioned. Accordingly, throughout thespecification and claims where the bottom of the hopper is referred to, the term ?bottom is .used in a broad sense-to include all interior surfaces of ;the hopper embracing the immersed portion .of the periphery of the applicator roll. By'thus accurately positioning the junctures and J "at the centerof :theroll, the draw-off pipe 23 can'be located directly therebeneath so .that any solid particle will be drawn off before it can be transferred to theapplicator roll. Furthermore, being able .to accurately locate .junctures and J makes it possible to locate the ends of the conduit 30 on opposite sides of these points with accuracy and still have them connecting contour lines of greatest differential for themost'efiective mixing action.

The beneficial use of a coating apparatus constructed in accordance .with this invention is illustrated by the following example. From a hopper with a .centeriroller clearance of A and clearances of A3 at each end, and with the solution inlets at 22 and 23 and the solution outlet at .22, a dispersion .of gelatin and :cellulose nitrate in essentially 60% acetone, 5% ethylene chloride, 2 /z% water, balance methanol, was applied to the surface of aaplasticized cellulose triacetate sheet. The solution was eirculatedfrom .outlet 22' to inlets Z2 and 23 by asystem of pumps, pipesand tanks called a circulating system and in which there were suitable filters to remove any solid material. .After the hopper was in use for four hours,

solid particles were noted in the hopper. Most of these remained in thehopper but occasionally one would transfer to the roll or bead andthen either make an undesirable repeating or continuous .mark..on the vtriacetate sheet or hetransferredtoithesheet to make an undesirable defect. While the hopper remained in operation, the piping "was quickly changed so that'the .solutioninlet' was now-pipes 22 andlZ and:the-outlet was 23. Within 15 minutes no solid particles were evidentin the hopper and .none were seen by intermittent examination for two weeks during which the hopper was continuously in use.

It is apparent from the noted example that so long as the solution is withdrawn fromthe hopper in the vicinity of, and preferably directly beneath, the juncture points I and J, then any solid particles which might enter the solution .in the hopper will be withdrawn before it can be transferred to the applicator roll. While for purposes of illustration we have chosen to show the solution 'as being fed into both ends of the hopper, this is not a material condition to the invention since the manner and the position at which-the solution is fedinto the hopper is immaterial to the operation of the present invention. The advantage derived from pitching the bottom of the hopper away from the center of the applicator .roll toward both ends of the roll is that it definitely locates .the position of juncture points I and J ratherthan :having these points vary over the distance defined by a length equal to the center third of the roll length. Definite positioning of juncture points I and 1 makes it possible :to accurately locate the draw-off pipe 23in the proper posi' tion and also makes it possihle'totlocatethe opposite ends of the mixing conduit 30 on oppositesides of the .juncture points I and J and as close as possible thereto :in order to take advantage of the maximum difference in contour elevation on opposite sidesof'the hopper.

While we have shown and described certain specific embodiments of our invention, we .are fully aware :that many modifications thereof are possible. Our invention, therefore, is not to be limited to :the precise 'details :of construction shownand described but is intended to cover all modifications coming within the scope of the appended claims.

Having thus described our inventiomwhat Weclaim as new and desire to secure by Letters 'Patentof the United States is:

1.:In a coating apparatus :the combination with an open-mouth hopper adapted to contain a supplyof coating solution; an applicator roll .rotatably mounted in said hopper with .a portion .of its periphery dipping .intosa'id solution in spaced relation with .the bottom of .said hopper; thebottom of said hopper pitchedzradially away from the roll periphery .to form an'elevated ridge portion located opposite the 'middleithird of said roll; meansifor rotating said roll; and means forcontinually.feedingisolution into said hopper and drawing it therefrom and including an outlet in the bottom of said ihopperadjacent the elevated ridgeportion.

2. A coating apparatus according to claim 1 in which said elevated ridge portion inthebottom of said hopper is located approximately at the longitudinalicenter of said roll and in which said outlet in the-bottom of said hopper is disposed directlybelow said ridge .portion.

3. A coating apparatus according to .claiml and including means for placing in direct communication a point'in the hopper at the upside .of thetroll 'on one-side of the longitudinal centerof said roll anda point in the hopper at the down side .of the roll .on .the other side of the longitudinal center of said roll.

4. In a :coating apparatus the combination with an open-mouth hopperadapted to'contain 'a'supply ofcoating solution; an applicator roll rotatably mounted ins-said hopper with a portion of its periphery dippinginto said solution in spaced relation with the bottom of said-hopper; the bottom .of said hopper pitched :radially .away from the roll periphery'toiform .an elevated ridgesportion located-opposite the middle third of said roll; means-for rotating said roll; and a conduit-having one :end .extending-into the hopperat the upside of the roll .on onezside of said ridge portion and the otherend extending tllllO the hopper at thedown sideof the roll on theother side of said ridge portion.

No references cited. 

